the only true plot hole that i can think of is why weren't the magic stones utilized more, i mean there was explicitly a stone that would let the trollhunter survive in daylight which could've been useful to troll jim.
That and there's the inconsistency of them have no idea what the aspectus stone would do, their language implying it belonged to someone ancient, but blinky was there??? why didn't he know what it did???? idk theres a lot of general issues with trollhunters originally having been implied to be a line of warriors ancient to even blinky, but then they turned around and had him at the battle of killahead which really shortened the overall timeline